It may have worked when the book was written. The evidence for this would be all the profitable landleeches around us who successfully get rich for doing very little. The people who followed this advice are the reason why housing prices are so high and the advice no longer works because they are so high.

However, the economic environment tends to change to cancel out things like this, in the long run. Look at the recent adjustment in the yen carry trade - the one that was blamed for the stock market crash last week. Lots of rich trading firms were borrowing billions of dollars in yen, at low rates, lending the dollars at high rates, making a profit in yen. However, after many years of this, the price of yen adjusted 12% overnight and wiped out all the profits and then some, from the firms that were still doing it. They had to spend all their dollar profits to get enough yen to pay the loans back. (They could have continued the trade, but the movement spooked them as the yen's value wasn't as stable as they thought and further movements could cause even bigger losses)

In the mortgage/rental scenario, this correction happens when the housing market declines, due to governments no longer preventing the necessary new construction of dense housing complexes. A tipping point will eventually be reached where landleeches are exiting their positions to cut their losses, causing prices to decline further causing more losses to remaining landleeches, who exit their positions to cut them.

Yeah I never totally got how anyone ever thought that shit was possible. I will say though that having rental property that you own outright is fantastic. Depreciation by itself is unbelievable. I'll make more than the initial purchase price of the property just in tax refunds.

Right. If you have the blue collar skills to maintain your apartment and the pink collar skills to manage the tenant relationships yourself it can be a great business. My brother-in-law owns a number of apartments close to where he lives and he does great.